In the manufacture of implants such as breast implants very high standards have to be met in a reproducible manner in terms of, for example, materials employed and processing details used. In addition, the dimension and the shape of an implant have to be obtained in a reliable manner within very narrow tolerances. Implants which do not meet such standards usually have to be discarded. Moreover, any sub-optimal implant may increase the risk of non-compliance with the patient and may even be rejected by the tissue of such patient. In case a breast implant is not accepted by the surrounding tissue there is a very high likelihood of so-called capsular contracture, that is, a hard sphere of collagen is formed around the implant thereby necessitating additional surgery.
It is believed that capsular contracture is caused, among others, by small pieces which have been broken off or have become separated from the surface or the shell of the implant. Further, it has been postulated that by use of structured or textured implant surfaces capsular contracture can be repressed either completely or at least for much longer periods of time compared to other types of implants.
Therefore, much effort has been spent in optimizing both the surface structure and/or material of an implant as well as its manufacture.
In U.S. Pat. No. 5,296,069 a process for the manufacture of implants is disclosed whose surfaces are coated with an amorphous material which shall not come loose thereby preventing capsular contracture. This process requires disposing a first and a second sheet assembly on the front and the back side of an implant being already filled with gel, i.e. to a finished implant, and which has smooth surfaces. Said first sheet assembly and said second sheet assembly have to be made from a non-vulcanized silicone sheet and a foam sheet. It is required to pass said sheet assembly through two parallel and spaced apart rollers so as to exert a predetermined pressure for adhering said assembly. It is the non-vulcanized silicone sheet which in each case faces the smooth surface of the implant. Where the two sheets come together, they go out away from the implant; it is not possible for them to curl under the implant. The joint overlapping portions of said first and second sheet assemblies need to be cut off thereby generating a circumferential seam in that section of the implant which is bridging its front and the back side. It has been found that such seam may not be well accepted by the tissue of the patient. Moreover, the process according to U.S. Pat. No. 5,296,069 does not eliminate the problem of folds, wrinkles or even voids being formed on or between the assembly sheets and the underlying implant. This process is therefore rather cumbersome and inefficient.
In FR 2,675,049 A1, a breast prosthesis is described where a specific polyether polyurethane is glued onto a silicone envelope filled with a silicone gel. In a similar manner in FR 2 677 539 A1 a polyurethane sheet is glued to a breast implant being made of elastomeric silicone material. In order to minimize the risk of capsular contracture it is proposed to glue a first polyurethane sheet onto the front side of the implant and a second polyurethane sheet to the backside of said implant and to leave a circumferential area uncovered by said polyurethane sheets which bridges the front and the back side of said implant.
Although it has been proposed for about 30 years to make use of textured surfaces, e.g. in the form of polyurethane foams for breast implants in order to reduce the risk of capsular contracture—as evidenced by S. Herman, Plastic & Reconstructive Surgery, 1984, pages 411 to 414, and J. A. Lilla and L. M. Vistmis, Plastic & Reconstructive Surgery 1976, pages 637 to 649,—efforts are still ongoing to increase patient compliance, comfort and safety. For example, in WO 2010/069019 A1 breast implants are described having independent expandable and interactive compartments and which have an external silicone membrane which can externally be coated with a Ricinus communis polyurethane foam covered with hydroxyapatite microcrystals or nanocrystals.
Thus, there still is a need to provide a manufacturing process which in itself guarantees to obtain high quality products in a reliable and reproducible manner while yet yielding affordable products.